Kerry: If the hammer is NOT hitting the nipple squarely, then use a grinding bit for a dremel tool to go into the skirt, and grind away the high side of the face of the hammer.
To test if the hammer is hitting squarely, fold over a piece of paper towel, and put it over the top of the nipple. Hold it in place while you cock and fire the hammer. Then lift the hammer off and inspect the paper towel. It should look like you have used a paper punch on the towel, with a nipple size hole, cut completely around the circumference of the nipple, in the toweling. Because paper towels have some cloth fibers in them, there is usually NOT a complete hole in the towel, but you will definitely see the ring of the top of the nipple where it cuts the paper. If you don't see a full ring or cut in the paper, the hammer is not hitting the nipple squarely, and you need to fix that for reliable ignition.
Based on testing lots of percussion locks at my gun club back when I was shooting a percussion lock, I believe most locks have hammers that do not hit squarely on the nipple. The alignment may be correct, side to side, and front to back, but the face of the hammer is rarely squared to the top edge of the nipple. The paper toweling " test " is the fastest and cheapest way to find out about any gun.
Find the high side by putting marking dye, or lampblack, or lipstick on the top edge of a NEW nipple. Then lower the hammer down to transfer the marking agent to the hammer. Grind away where the agent appears on the face of the hammer.
Repeat the procedure until you get a full, wide circle(ring) of agent showing on the face. That indicates that the hammer is NOW striking the nipple squarely.
If you are using the right sized caps for the nipple, and the nipple is in good condition, the caps should all fire reliably, and because the hammer is now hitting the top of the nipple squarely, and the entire circumference of the edge of the nipple is taking the hammer blows, you are less likely to see the nipple being bulged, or peened over on one side or the other. Invest in the Bronze, AMPCO nipple for the gun when you can. They are actually tougher than the steel nipples, and seem to last forever! :thumbsup: